Chapter 3: Cells and Tissues

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1)Define cell. A cell is the structural and functional units of all living things 2)According to the cell theory, what the organism can do depends on ... What its cells can do. 3)Name the three basic parts of a cell, and give the location of each. Plasma membrane = external barrier that regulates what enters and leaves the cell. Cytoplasm = the area where most cell activities occur. Nucleus = control center of the cell. 4)How would you explain the meaning of a "generalized cell" to a classmate? The generalized cell is a concept that describes organelles and functions common to all cells. 5)What is the general function of nucleoli? Nucleoli are the sites of synthesis of ribosomes, which are important in protein synthesis. 6)Why do phospholipids organize into a bilayer, tail to tail, in a watery environment? The phospholipids have both polar (heads) and nonpolar (tails) regions. Polar aligns with polar (water and other polar molecules inside and outside the cell). Nonpolar aligns with nonpolar in the membrane interior. 7)The external faces of some membrane proteins have sugar groups attached to them. What are three roles these sugar-coated proteins play in the life of a cell? They act as receptors, determine blood type, and play a role in cell-to-cell interactions. 8)What is the special function of gap junctions? Of tight junctions? Communication and binding together. 9)How do the cytosol and the cytoplasm differ? The cytosol is the liquid portion of the cytoplasm. Cytoplasm includes cytosol, organelles, and inclusions. 10)Which two organelles are sacs of enzymes, and what is the function of each of these organelles? Lysosomes break down ingested bacteria, worn-out organelles, and dead cells. Peroxisomes detoxify a number of harmful toxic substances and disarm free radicals. 11)Which organelle is the major site of ATP synthesis? Which packages proteins? Mitochondria are the major site of ATP synthesis. The Golgi apparatus is the packaging site. 12)Which two types of cytoskeletal elements are involved in cell mobility? Microtubules and microfilaments are involved in cell mobility. 13)Which of the cytoskeletal elements is the basis of centrioles? Of microvilli? The basis of centrioles is microtubules; Microvilli is a core of actin filaments. 14)The major function of cilia is to move substances across the free cell surface. What is the major role of microvilli? Microvilli increase the cell surface area for absorption. 15)Name the two cell types involved in connecting body parts or regions. Fibroblasts and erythrocytes. 16)What is the main function of a neuron? Gather information and control body functions. 17)What is the energy source for all types of diffusion? Kinetic energy 18)What determines the net direction of any diffusion process? The concentration gradient determines the direction that water and solutes move by diffusion. Movement is from high to low concentration of a given substance. 19)What are the two types of facilitated diffusion, and how do they differ? A channel protein is an opening formed by membrane proteins for diffusion of certain small solutes. A carrier protein undergoes shape changes that allow diffusion of a specific substance through the membrane. 20)Explain the phrase "move down the concentration gradient." Means to move from where there is a lot of something (high concentration) to where there is not a lot (low concentration). 21)What happens when the Na+-K+ pump is phosphorylated? When K+ binds to the pump protein? When the pump protein is phosphorylated, it changes shape. When K+ binds, phosphate is released. 22)Which vesicular transport process moves large particles into the cell? Phagocytosis moves large particles into the cell. 23)Which process is more selective—pinocytosis or receptor-mediated endocytosis? Receptor-mediated endocytosis. 24)How do the terms template strand and complementary relate to DNA synthesis? DNA is double-stranded. When it is replicated, each strand serves as a template to build a complementary strand. Thus, if the template strand is ACT, the complementary strand formed at that site is TGA. 25)What is cytokinesis? What results if cytokinesis does not happen? Cytokinesis is the division of the cytoplasm. If cytokinesis does not occur, the result is a binucleate cell. 26)What is the role of mRNA in protein synthesis? What about tRNA? mRNA carries the coded information for building proteins from the DNA to the ribosome where protein synthesis occurs. tRNA delivers amino acids to the ribosome and "checks" the location by recognizing the mRNA codon with its anticodon. 27)What are the two stages of protein synthesis, and in which stage are proteins actually synthesized? What occurs in the other stage? Transcription and translation. Proteins are synthesized during translation. Transcription is the production of mRNA using DNA as a template. 28)What two criteria are used to classify epithelial tissues? Cell shape and cell arrangement (layers) 29)How do endocrine and exocrine glands differ in structure and function? Exocrine glands have ducts that carry their secretion (typically a protein-containing secretion other than hormones) to a free body surface. Endocrine glands produce only hormones and are ductless glands. 30)Which of the following properties apply to epithelial tissues? Can repair itself; cells have specialized cell junctions. 31)Which two characteristics are hallmarks (distinguishing characteristics) of epithelial tissue? Having one free surface and being avascular. 32)What are the two hallmarks of connective tissue? Variations in blood supply and the production of a nonliving, extracellular matrix that surrounds their living cells. 33)Which fiber type contributes strength to connective tissues? Collagen fibers. 34)Which muscle type(s) is(are) injured when you pull a muscle while exercising? Skeletal muscle. 35)How does the extended length of a neuron's processes aid its function in the body? It allows neurons to control structures some distance away. 36)Nervous tissue is irritable. What does this mean? Nervous tissue is irritable, meaning it is able to respond to stimuli. 37)Which tissue type is the basis for scar tissue? Dense fibrous connective tissue 38)Which of the four types of tissue is most likely to remain mitotic throughout life? Epithelium and some connective tissues remain mitotic. 39)What cellular error allows a neoplasm to form? It is an abnormal growth that occurs when normal control of cell division is lost; this was also described as "mitosis gone wild." 40)How does the activity of endocrine glands change as the body ages? Endocrine activity tends to decline with age.

Active Transport

Active transport called solute pumping uses ATP to energize its protein carriers, which are called solute pumps. The sodium-potassium (Na+-K+) pump alternately carries sodium ions (Na+) out of and potassium ions (K+) into the cell. This process is absolutely necessary for normal transmission of nerve impulses.

Cells

Are the structural units of all living things, from one-celled organisms such as amoebas to complex multicellular organisms such as humans, dogs, and trees. The human body contains 50 to 100 trillion of these tiny building blocks.

Organelles

Are specialized cellular compartments, that are the metabolic machinery of the cell. -Mitochondria are usually depicted as tiny, lozenge-like or sausage-shaped organelles and in living cells they lengthen and change shape almost continuously -Ribosomes are tiny, bilobed, dark bodies made of proteins and one variety of RNA called ribosomal RNA, are the actual sites of protein synthesis in the cell. -Endoplasmic reticulum ; "network within the cytoplasm"), or ER, is a system of fluid-filled tunnels (or canals) that coil and twist through the cytoplasm. It is continuous with the nuclear envelope and accounts for about half of a cell's membranes. It serves as a mini circulatory system for the cell because it provides a network of channels for carrying substances (primarily proteins) from one part of the cell to another. Rough endoplasmic reticulum is so called because it is studded with ribosomes. All of the building materials of cellular membranes are formed either in it or on it, "cell's membrane factory." Smooth endoplasmic reticulum communicates with the rough variety, it plays no role in protein synthesis, because it lacks ribosomes. Instead it functions in lipid metabolism (cholesterol and fat synthesis and breakdown) and detoxification of drugs and pesticides. -Golgi apparatus appears as a stack of flattened membranous sacs that are associated with swarms of tiny vesicles. ound close to the ER and is the principal "traffic director" for cellular proteins. Its major function is to modify, package, and ship proteins (sent to it by the rough ER via transport vesicles) in specific ways, depending on their final destination -Lysosomes, which appear in different sizes, are membranous "bags" containing powerful digestive enzymes. "cellular stomachs." -Peroxisomes are membranous sacs containing powerful oxidase enzymes that use molecular oxygen (O2) to detoxify a number of harmful or poisonous substances, including alcohol and formaldehyde. "disarm" dangerous free radicals (highly reactive chemicals with unpaired electrons that can damage the structure of proteins and nucleic acids). - Cytoskeleton, acts as a cell's "bones and muscles" by furnishing an internal framework that determines cell shape, supports other organelles, and provides the machinery for intracellular transport and various types of cellular movements. Made up of microfilaments, intermediate filaments, and microtubules. -Centrioles, collectively called the centrosome, lie close to the nucleus; They are rod-shaped bodies that lie at right angles to each other; internally they are made up of a pinwheel array of nine triplets of fine microtubules. Role in generating microtubules and also for directing the formation of the mitotic spindle during cell division.

Hydrophobic

Nonpolar fatty acid "tails,"("water fearing"), avoid water and line up in the center (interior) of the membrane.

Generalized Cell

The cells typical features: All cells have 3 main regions, a nucleus, a plasma membrane, and the cytoplasm. -The nucleus is usually located near the center of the cell. It is surrounded by the semifluid cytoplasm, which in turn is enclosed by the plasma membrane, which forms the outer cell boundary.

Nucleus

The cells, "headquarters," or the control center. Nucleus envelope or Nuclear membrane: the double membrane barrier of the nucleus; separates the nucleoplasm from the cytoplasm. Nuclear pores: two layers of the nuclear envelope fuse, generating openings Nucleoli: one or more small, dark-staining, essentially round bodies; sites where cell structures called ribosomes are assembled

Passive Processes: Diffusion and Filtration

Diffusion is an important means of passive membrane transport for every cell of the body. Filtration, generally occurs only across capillary walls. Diffusion is the process by which molecules (and ions) move away from areas where they are more concentrated (more numerous) to areas where they are less concentrated (with fewer of them). Molecules will diffuse through the plasma membrane if The molecules are small enough to pass through the membrane's pores (channels formed by membrane proteins). The molecules are lipid-soluble. The molecules are assisted by a membrane carrier.

Diffusion

Diffusion is the process by which molecules (and ions) move away from areas where they are more concentrated (more numerous) to areas where they are less concentrated (with fewer of them). Molecules will diffuse through the plasma membrane if : The molecules are small enough to pass through the membrane's pores (channels formed by membrane proteins). The molecules are lipid-soluble. The molecules are assisted by a membrane carrier. *concentration gradient

Filtration

Filtration is the process by which water and solutes are forced through a membrane (or capillary wall) by fluid, or hydrostatic, pressure. * pressure gradient

Vesicles

Transport vesicles areas of the cell in small "sacs" of membrane, that carry substances around the cell. Secretory vesicles, which travel to the plasma membrane.

Vesicular Transport

Vesicular transport, which involves help from ATP to fuse or separate membrane vesicles and the cell membrane, moves substances into or out of cells "in bulk" without their actually crossing the plasma membrane directly. The two types of vesicular transport are exocytosis and endocytosis. -Exocytosis "out of the cell" is the mechanism that cells use to actively secrete hormones, mucus, and other cell products or to eject certain cellular wastes. -Endocytosis "into the cell" includes those ATP-requiring processes that take up, or engulf, extracellular substances by enclosing them in a vesicle can be phagocytosis "cell eating" pinocytosis "cell drinking" Receptor-mediated endocytosis is the main cellular mechanism for taking up specific target molecules; In this process, receptor proteins on the plasma membrane bind exclusively with certain substances.

Cell Diversity

*Cells that connect body parts: -Fibroblast. This cell has an elongated shape, like the cable-like fibers that it secretes. It has an abundant rough ER and a large Golgi apparatus to make and secrete the protein building blocks of these fibers. -Erythrocyte (red blood cell). This cell carries oxygen in the blood. Its biconcave disc shape provides extra surface area for the uptake of oxygen and streamlines the cell so it flows easily through the bloodstream. So much oxygen-carrying pigment is packed in erythrocytes that all other organelles have been shed to make room. *Cells that cover and line body organs: -Epithelial cell. The hexagonal shape of this cell is exactly like a "cell" in a honeycomb of a beehive. This shape allows epithelial cells to pack together in sheets. An epithelial cell has abundant intermediate filaments and desmosomes that resist tearing when the epithelium is rubbed or pulled. *Cells that move organs and body parts: -Skeletal, cardiac, and smooth muscle cells. These cells are elongated and filled with abundant contractile filaments, so they can shorten forcefully and move the bones, pump blood, or change the size of internal organs to move substances around the body. *Cell that stores nutrients: -Fat cell. The huge spherical shape of a fat cell is produced by a large lipid droplet in its cytoplasm. *Cell that fights disease: -White blood cells such as the macrophage (a phagocytic cell). This cell extends long pseudopods ("false feet") to crawl through tissue to reach infection sites. The many lysosomes within the cell digest the infectious microorganisms (such as bacteria) that it "eats." *Cell that gathers information and controls body functions: -Nerve cell (neuron). This cell has long processes (extensions) for receiving messages and transmitting them to other structures in the body. The processes are covered with an extensive plasma membrane, and a plentiful rough ER synthesizes membrane components and signaling molecules called neurotransmitters. *Cells of reproduction: Oocyte (female). The largest cell in the body, this egg cell contains several copies of all organelles, for distribution to the daughter cells that arise when the fertilized egg divides to become an embryo. Sperm (male). This cell is long and streamlined, built for swimming to the egg for fertilization. Its flagellum acts as a motile whip to propel the sperm.

Cell Extensions

-Cilia "eyelashes" are whiplike cellular extensions that move substances along the cell surface. -Flagella long, whiplike extensions of the cell membrane of some bacteria and sperm; serve to propel the cell. -Microvilli "little shaggy hairs" are tiny, fingerlike extensions of the plasma membrane that project from an exposed cell surface. They increase the cell's surface area tremendously and so are usually found on the surface of cells active in absorption such as intestinal and kidney tubule cells.

Cytosol and Inclusions

-Cytosol is semitransparent fluid that suspends the other elements. Dissolved inside the largely water are nutrients and a variety of other solutes; dissolved substances. -Inclusions are chemical substances that may or may not be present, are stored nutrients or cell products floating in the cytosol including ipid droplets common in fat cells, glycogen granules abundant in liver and muscle cells, pigments such as melanin in skin and hair cells, mucus and other secretory products, and various kinds of crystals. "cellular pantry"

Types of Cell Membrane Junctions

-Tight junctions are impermeable junctions that encircle the cells and bind them together into leakproof sheets. "Zipper" (e.g. In the small intestine these junctions prevent digestive enzymes from seeping into the bloodstream. -Desmosomes are anchoring junctions scattered like rivets along the sides of adjacent cells. They prevent cells subjected to mechanical stress (such as heart muscle cells and skin cells) from being pulled apart. "buttonlike thickenings" -Gap junctions, or communicating junctions, function mainly to allow communication. These junctions are commonly found in the heart and between embryonic cells. In gap junctions, the neighboring cells are connected by hollow cylinders composed of proteins (called connexons) that span the entire width of the abutting membranes (which are therefore called transmembrane proteins).

Multiple Choice Questions

1)Which of the following would you expect to find in or on cells whose main function is absorption? Microvilli 2)Adult cell types you might expect to have gap junctions include heart muscle. 3)Which of the following are possible functions of the glycoproteins in the plasma membrane? Determination of blood groups, Binding sites for toxins or bacteria and Aiding the binding of sperm to egg 4)A cell with abundant peroxisomes would most likely be involved in detoxification activities. 5)A cell stimulated to increase its steroid production will have abundant smooth ER. 6)For diffusion to occur, there must be some sort of carrier system. 7)In which of the following tissue types might you expect to find goblet cells? Simple columnar 8)Which epithelium is "built" to withstand friction? Stratified squamous 9)What kind of connective tissue acts as a sponge, soaking up fluid when edema occurs? Areolar connective 10)What type of connective tissue prevents muscles from pulling away from bones during contraction? Dense connective 11)Which of the following terms describe cardiac muscle Striated, Intercalated discs, Involuntary and Branching 12)Cancer is the same as all malignant neoplasms.

Plasma Membrane or cell membrane or cytoplasmic membrane

A fragile, transparent barrier that contains the cell contents and separates them from the surrounding environment.

Cell Theory

Four Concepts: -A cell is the basic structural and functional unit of living organisms. -The activity of an organism depends on the collective activities of its cells. -According to the principle of complementarity, the activities of cells are dictated by their structure (anatomy), which determines function (physiology). -Continuity of life has a cellular basis.

Cytoplasm

Is the cellular material outside the nucleus and inside the plasma membrane; the site of most cellular activities. "factory floor of the cell"

Events of Cell Division

Mitosis is the process of dividing a nucleus into two daughter nuclei with exactly the same genes as the "mother" nucleus. Prophase. As cell division begins, the chromatin threads coil and shorten so that the barlike chromosomes become visible under a microscope. Because DNA has already been replicated, each chromosome is actually made up of two identical strands called sister chromatids , held together by a small buttonlike body called a centromere . The centrioles separate from each other and begin to move toward opposite sides of the cell, directing the assembly of a mitotic spindle (composed of microtubules) between them as they move. The spindle provides scaffolding for the attachment and movement of the chromosomes during the later mitotic stages. By the end of prophase, the nuclear envelope and the nucleoli have broken down and temporarily disappeared, and the chromosomes have attached randomly to the spindle fibers by their centromeres. Metaphase. In this short stage, the chromosomes line up at the metaphase plate (the center of the spindle midway between the centrioles) so that a straight line of chromosomes is seen. Anaphase. During anaphase, the centromeres that have held the chromatids together split. The chromatids (now called chromosomes again) begin to move slowly apart, drawn toward opposite ends of the cell. The chromosomes seem to be pulled by their half-centromeres, with their "arms" dangling behind them. This careful division of sister chromatids ensures that each daughter cell gets one copy of every chromosome. Anaphase is over when the chromosomes stop moving. Telophase; Telophase is essentially prophase in reverse. The chromosomes at opposite ends of the cell uncoil to become threadlike chromatin again. The spindle breaks down and disappears, a nuclear envelope forms around each chromatin mass, and nucleoli appear in each of the daughter nuclei. Cytokinesis, or the division of the cytoplasm, usually begins during late anaphase and completes during telophase.

Membrane Transport

Solution is a homogeneous mixture of two or more components. (e.g. the air we breathe (a mixture of gases), seawater (a mixture of water and salts), and rubbing alcohol (a mixture of water and alcohol). Solvent the substance present in the largest amount in a solution. Solute the dissolved substance in a solution. Intracellular fluid (collectively, the nucleoplasm and the cytosol) is a solution containing small amounts of gases (oxygen and carbon dioxide), nutrients, and salts, dissolved in water. extracellular fluid, or interstitial fluid, the fluid that continuously bathes the exterior of our cells; contains thousands of ingredients, including nutrients (amino acids, sugars, fatty acids, vitamins), regulatory substances such as hormones and neurotransmitters, salts, and waste products. Selective permeability means that a barrier allows some substances to pass through it while excluding others. Thus, it allows nutrients to enter the cell but keeps many undesirable or unnecessary substances out.

Cell Division

The cycle has two major periods: interphase, in which the cell grows and carries on its usual metabolic activities, and cell division, during which it reproduces itself.

Hydrophilic

The polar "heads" of the lollipop-shaped phospholipid molecules, ("water loving") and are attracted to water, the main component of both the intracellular and extracellular fluids, and so they lie on both the inner and outer surfaces of the membrane.

Fluid Mosaic Model

The structure of the plasma membrane consists of two phospholipid (fat) layers arranged "tail to tail," with cholesterol and floating proteins scattered among them, may also have sugar groups attached, forming glycolipids. Phospholipids are polar molecules: The charged end interacts with water, and the fatty acid chains do not. Polarity that makes phospholipids a good foundation for cell membranes.

Chromatin

The structures in the nucleus that carry the hereditary factors (genes). "beads on a string" -Chromosomes: barlike body of tightly coiled chromatin; visible during cell division. "rodlike bodies"